A satellite-based radio system which operates with only a small number of satellites in distributed orbits is used, in particular in the USA. The aim is to offer antennas for this satellite-based radio system which have to provide the same minimum gain even at low elevation angles from 25° up to an elevation of 90°.
At the same time, the combination antennas are also intended to be suitable for receiving terrestrial signals.
The corresponding systems are also known in the specialist field by the expression SDARS services, which transmit in the 2.3 GHz band. The satellite signals are in this case transmitted with circular polarization.
In order to take account of these extreme conditions and to provide a high antenna gain even at low elevations of 25° or more, continuous attempts have been made to take account of these extreme requirements by specially adapted antenna structures.
A special antenna system has thus become known on the USA market, which contains a cruciform dipole that is formed from a flat material and thus forms four quadrants which are separated from one another by the dipole walls. A separate, vertically extending monopole is then arranged in each quadrant, via which the terrestrially transmitted vertically polarized signals can be received. However, the overall complexity of the antenna is considerable since, in particular, appropriate feed networks are also required in order to feed the cruciform dipole and the four monopoles.
The publication “A Combination Monopole/Quadrifilar Helix Antenna For S-Band Terrestrial/Satellite Applications” in the Microwave Journal May 2001 likewise describes a combination antenna which is intended to be suitable for satellite reception on the basis of the SDARS services in the USA. This antenna is likewise intended to have a good antenna gain and a sufficiently good axis ratio even at elevation angles of around 25°. These antennas have a rod monopole which extends vertically, and around which a helix is arranged.
Finally, however, EP 1 100 148 A1 also discloses a correspondingly circular polarized cross dipole antenna, which has two pairs of inverted V-shaped dipole antenna arrangements. These antenna dipole elements are curved like an inverted “V”.